This invention relates in general to devices for illuminating the site of microsurgery, in particular eye surgery, and, more specifically, to a microsurgery ring illumination system.
Conventional surgical microscopes are stereoscopic, having a large objective lens oriented adjacent to the microsurgery site. Entrance pupils are spaced across the objective lens to collect a stereo image off the single, large diameter, long working distance objective lens. Powerful and bright illumination systems are provided to illuminate the surgical field. Some use an oblique system, where the light source is adjacent to the objective lens housing and is angled at the surgical field. Others mount the light adjacent to, and somewhat coaxial with, the entrance pupils. Typically they are powered with a halogen light bulb, sometimes with a fiber optic system conveying light from a remote source.
These illumination systems have a number of drawbacks. Shadows are created if a hand or instrument blocks the light path, often obscuring critical areas of the surgical field. The lighting is non-uniform due to the essentially single point light source at an angle to the microscope optical pathways, resulting in overly bright light on the source side, falling off to insufficient light on the other side. Even more significantly, glare from reflections off instruments or devices (or even tissue and fluids) inhibit the surgeons visualization and can adversely affect surgical efficiency. These problems are of particular importance in eye surgery where seeing transparent membranes is critical. Due to poor light delivery, surgeons are forced to turn the lights to near maximum levels to see the internal structures in, for example, cataract surgery. By doing so, however, they greatly increase surface glare from the fluids at the surface of the eye, seriously degrading their sight. This combination of overly bright lights and glare is uniformly disliked by surgeons and may be damaging to the sight of the surgeons getting such large lumen doses in his/her eyes.
A coaxial light source, from the patient's perspective, is much like looking into the sun. It has long been established that harm is done to retinas during eye surgery due to the light conditions. Retinal damage may manifest as light sensitivity, or photophobia, photic maculopathy (transient partial vision loss) due to exposure to intense light and sometimes cystoid macular edema (CME) which is essentially hardening of the arteries in the eye. CME is particularly devastating because it destroys the function of the most central vision and highest acuity of the macula. In essence, the high light level burns the retina.
Commonly, about a 2% CME rate is attributed to cataract surgery, although other factors in addition to high light intensity such as posterior capsule rupture can contribute to CME. Some studies indicate that angiographic postoperative CME of up to 25-30% can occur. This may manifest as subclinical losses in contrast sensitivity, color loss, etc.
In many types of eye surgery the eye is not injected with an anesthetic to deaden the eye. Some eye surgeries such as radial keratotomy, pterygium removal and certain new cataract techniques are performed under topical anesthesia, leaving the patient with normal ocular function during surgery. Often, these patients cannot tolerate the high intensity prior art microscope lights.
Thus, there is a continuing need for improved systems for lighting the site of microsurgery, in particular for eye surgery which use much lower and more uniform light intensities, reduce or eliminate shadows on the surgery field from instruments or the like, greatly reduce glare from instruments and surface fluids, reduce high intensity light damage to the surgeons's eyes and, in the case of eye surgery, reduce or eliminate light damage to the patient's eye. In addition, the light pattern would desirably aid in surgical and diagnostic procedures, such as those using conventional slit-lamps.